Mom doesn't get its a bad idea...

A bit of background:
My mom has a 3 (ish) Autralian Shepard/ Springer Spaniel mix, named Casanova. They got him from a yard sale. The lady was moving and had to give him, his two siblings and mother away. For the first two months my mom and her fiance had this dog all was good. I could go over whenever and let myself in the house without a problem. Then one day, while playing fetch in the yard, Casanova starts to chase the toy then turns and comes charging at me, teeth bared, snarling, barking. He actually got ahold of my jeans before I could get away. Thinking it was a fluke, I went back to their place that night to get some money for gas. Once again, the dog went after me. This time mom's fiance had to grab him to keep him from biting me. Since that day whenever I come in the yard he goes stock still, tail straight out, head down, teeth bared, then full blown barking and growling. My mother tells me he's not gonna bite. She also tells me he is going great at meeting other dogs. "Oh he loves other dogs. He is just really excited to meet them" where her words.
So I, after much pestering from her, took my 3 year old Husky over to meet him. I knew it wasn't going to go like she planned. Of course, as soon as Tiberius got even close to Casanova, Casanova went from happy tail wagging to snarling, barking and trying to bite. Gordon, Mom's fiance, had a good hold on his leash thankfully. Tiberius just ran behind me, and leaned into my legs.

So bringing Tiberius over there was mistake number one. She understands that now. Her next idea is to take both dogs on a walk together. I won't go into her house if Casanova is inside. I don't trust him. How can I explain to her that this isn't the best of ideas? I know she is just trying to help socialize Tiberius...but I don't want to be within 100ft of her dog especially when she can't keep hold of him on a leash. Thanks in advance.